This invention is generally directed to photoresponsive imaging members, and more specifically the present invention is directed to layered photoresponsive imaging members with a hole transporting layer comprised of certain fluorenes. Thus, in one embodiment the present invention relates to an imaging member comrprised of a photogenerating layer, and a hole transport layer comprised of bis(diarylamino)fluroenes Further, in another embodiment of the present invention there is provided an imaging member comprised of a supporting substrate, a hole transport layer comprised of bis(diarylamino)fluorenes, and situated therebetween a photogenerating layer. Additionally, the present invention includes within the scope thereof imaging members wherein the photogenerating layer is situated between the hole transporting layer, and the supporting substrate. The photoresponsive imaging members of the present invention are useful for incorporation into various imaging systems, particularly xerographic imaging processes wherein, for example, the members are initially charged negatively, and development is accomplished by dry or liquid developer compositions. Also, the aforementioned fluorene derivatives of the present invention possess superior hole transport properties and can be economically prepared. Furthermore, the layered photoresponsive imaging members of the present invention are durable and are insensitive to changes in environmental conditions such as humidity and temperature.
The generation and development of electrostatic latent images on the surfaces of photoconductive materials by electrostatic means is well known. One electrostatic method involves the formation of a latent image on the surface of a photoreceptor. The photoreceptors can be comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material, and in many instances there can be incorporated therein a thin barrier layer between the substrate and the photoconductive layer to prevent charge injection into the photoconductive layer upon charging of its surface, which injection would adversely effect the quality of the resulting image.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, which can function as both a photogenerating and hole transporting substance, or composite layered devices, with a photoconductive substance dispersed in other substances. An example of one type of composite photoconductive layer used in xerography is discribed, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
There are also known photoreceptor materials comprised of other inorganic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptors are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus for increased performance. Additionally, positively charged layered photoresponsive imaging members are needed for generating images of acceptable resolution, and substantially no undesirable background deposits.
Recently, there has been disclosed layered photoresponsive devices comprised of generating layers and aryl amine hole transport layers, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Examples of generating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of the active transport layer molecules that may be employed are comprised of the aryl amines illustrated therein. The imaging members of the present invention are similar to those described in the aforementioned patent with the primary exception that there are selected in place of the aryl amines the fluorene derivatives illustrated herein, which fluorenes possess improved characteristics, including permitting the more rapid transport of holes. Furthermore, the fluorene hole transport molecules of the present invention possess excellent compatibility with common polymer binders such as polycarbonates, polyesters, poly(methyl methacrylate), polystyrene copolymers, and the like, thus ensuring excellent long-term stability of the transport layers. Moreover, the fluorene derivative hole transport compounds selected for the imaging members of the present invention can be economically obtained by simple synthetic processes, and wherein the products resulting are of exceptionally high purity thus enabling them to be very suitable for xerographic imaging methods.
Other representative prior art disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116; 4,047,949; 4,081,274 and 4,315,981. According to the disclosure of the U.S. Pat. No. 4,315,981, the recording member consists of an electroconductive support, a photoconductive layer of organic materials which contain a charge carrier producing dyestuff layer of a compound having an aromatic, or heterocyclic polynuclear quinone ring system, and a charge transport layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members comprised of 7-nitro-2-aza-9-fluorenylidene-malononitrile as charge transporting substances. According to the disclosure of this patent, the electrographic light sensitive members are comprised of an electroconductive support, a layer thereover of a photogenerating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile of the formula, for example, as illustrated in column 1. There are also disclosed in U.S. Pat. No. 4,474,865 imaging members with electron transporting layers of fluorenylidene derivatives. In addition, there are also known layered photoresponsive imaging members wherein there are selected hole transport layers of aryl amines, and various photogenerating squaraine compounds, reference for example U.S. Pat. Nos. 4,552,822; 4,415,639; 4,471,041; and 4,486,520
There are also illustrated in U.S. Pat. No. 4,618,551, the disclosure of which is totally incorporated herein by reference, photoresponsive imaging members with photogenerating layers, and charge transport layers comprised of polysilylenes. More specifically, there is illustrated in the aforementioned patent a polysilylene hole transporting compound for use in imaging members, which compound is of the formula as illustrated in claim 1 with specific examples of polysilylenes being poly(methylphenylsiylene) of an average molecular weight of greater than 50,000.
Also of particular interest is U.S. Pat. No. 4,106,934, which illustrates photoconductive insulating compositions containing one or more p-type organic photoconductor components and a charge transfer complex of one or more electron accecptor components of the formulas as illustrated in the Abstract, for example. Particularly useful as Formula 1 type compounds are those materials as illustrated in column 5, beginning at line 30. Further, the use of N-substituted polymeric acrylic acid amides and alpha-alkyl acid amides as overcoatings for photoconductors is illustrated in U.S. Pat. No. 3,307,940 (see Formula 5, column 2). Moreover, fluorenylidene derivatives as charge transporting compounds in photoreceptors are disclosed in U.S. Pat. Nos. 4,400,455; 4,245,021; 4,415,640; 4,559,287 and 4,562,132. In addition U.S. Pat. No. 3,615,412 discloses organic photoconductors with certain fluorenes fused to benzo and naphtho ring structures, reference columns 1 to 3.
In addition, of interest is copending application U.S. Ser. No. 061,247, filed June 2, 1987, which illustrates imaging members with hydroxy fluorene derivatives, which derivatives are similar to those of the present invention with the exception that they contain thereon two hydroxy groups. Other copending applications filed June 1987, and disclosing imaging members with fluorene polymers are U.S. Ser. Nos. 061,064; 061,052; 061,248 and 061,053.
Although imaging members with various hole transporting substances, including aryl amines and polysilylenes, are suitable for intended purposes, there continues to be a need for the development of improved members, particularly layered members which are comprised of aminofluroene transport layers; and which members are insensitive to the changes in environmental conditions. Moreover, there continues to be a need for specific layered imaging members which not only generate acceptable images, but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members wherein the materials employed for the respective layers, particularly the hole transporting layer, are substantially inert to the users of these members. Further, there continues to be a need for improved photoresponsive imaging members which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these imaging members in repetitive imaging processes. Also, there continues to be a need for new hole transporting compounds that, when dispersed in polymeric matrices, are also useful as protective overcoating layers, and as interface materials for various imaging members. There also is a need for new hole transporting substances which enable increased mobility of holes in layered imaging members. Likewise, there is a need for hole transporting layers with increased stability, for example, wherein there is essentially no bleeding and segregation or crystallization of the transport molecules from the layers after extended usage. Furthermore, there is a need for hole transporting compounds useful in layered imaging members, which compounds are superior insulators in the dark compared to many other known hole transporting compounds, thus enabling charging of the resulting imaging member to higher fields while maintaining cyclic stability, and allowing improved developability. Additionally, there is a need for enabling the preparation of imaging members with new hole transporting compounds wherein the preparation allows for the selection of a variety of solvents, inclusive of toluene, benzene, tetrahydrofuran, cyclohexane, and halogenated solvents in addition to methylene chloride. There is also a need for imaging members with improved electrical characteristics, and comprised of fluorene hole transporting compounds, which members can be positively or negatively charged depending on the configuration of the member. Another need of the present invention resides in the provision of a novel class of fluorene hole transport molecules whose physical, electrical and electrochemical properties can be modified by altering the two carbon-9 substituents. Moreover, there continues to be a need for a simple synthetic process for the preparation of fluorene hole transporting compounds useful in the layered imaging members of the present invention.